As of January 22, 2021, the To Do application is only available via the web: https://to-do.office.com/tasks and only for reading information. All edits will not be saved and will be lost after logging out. From February 22, 2021, the To Do application will only be available to users with an Exchange Online / Office365 mailbox. If this change applies to you, do not forget to back up the data from To Do in advance. More information here.
This change does not affect the schedules in the Planner that appear in the Tasks application in Teams.
The information is intended for users with a university mailbox in Exchange (does not apply to users with a mailbox in Exchange Online / Office365).